BUKH DV20 overheat alarm

[winsbury]

Just bought a boat with a BUKH DV20 which is giving a feint (read: very annoying) overheat alarm sound but no indicator light once the engine is up to working temperature. The temperature sender has two spade connectors but only one cable. One spade seems to be permanently open circuit while the other varies between around 470 and 550 ohms cycling in unison with the thermostat as evidenced by slightly steaming water leaving the exhaust at the lower resistance readings. The engine is pumping plenty of water and the block is never too hot to touch. There is only one cable from the temp sender and if I ground it the alarm sounds at full volume and the blue overheat light comes on as expected.

I think the problem is one of the following:

1. cable connected to wrong temp sender connector however the spades are different sizes and the cable is connected to the matching size (larger) one.
2. temp sender faulty/incorrect resistance: BUKH does not have any technical information available but at £74+vat+delivery its an expensive item to change without being certain.
3. thermostat opening too late: BUKH suggested a test for this but also think because the block remains touchable it is unlikely again this is a remarkably expensive item at £64 plus £12 for the o-ring +vat+delivery.
4. fouling of waterways requiring Rydlime treatment: again this seems unlikely as block remains touchable and waterflow through exhaust is plentiful.

Does anyone have any technical data or can do some resistance measurements a known working temperature sender as this is my prime suspect ?

 

[Mort]

Its a well known issue with the DV20, I had the same issue. if you are handy with a soldering iron you can buy the parts from places like maplin, its the distribution plate, type inadee, diode and dv20 into google and there is a handy website describing the fault and how to fix it,

 

[winsbury]

Thanks Mort that's interesting - I assume you mean http://inadee.co.uk/fulmar.htm#Change of Distribution Plate in %20Operating%20Panel . I first noticed this after we had been on shore power for a few days and the batteries were fully topped up so think you may well be onto something there.

The thread below also states the warning light and sounder circuit should be on the smaller of the two spades, with the larger one supposed to connect to a temperature readout which mine does not have. Can you confirm this ?
http://www.ybw.com/forums/showthread.php?325540-BUKH-DV20-Temperature-sender-Faulty

 

[Mort]

Yes its a very annoying alarm to be going off all the time, since changing mine it hasn't done it since, except when it did overheat
My temp sensor appears to be different with only one central connector but I know it works. I have the full instrument panel gauges to fit soon so I realize I will need to buy the sensor with the two outputs when I do for the alarm and the gauge.

 

[VicS]

Just bought a boat with a BUKH DV20 which is giving a feint (read: very annoying) overheat alarm sound but no indicator light once the engine is up to working temperature. The temperature sender has two spade connectors but only one cable. One spade seems to be permanently open circuit while the other varies between around 470 and 550 ohms cycling in unison with the thermostat as evidenced by slightly steaming water leaving the exhaust at the lower resistance readings. The engine is pumping plenty of water and the block is never too hot to touch. There is only one cable from the temp sender and if I ground it the alarm sounds at full volume and the blue overheat light comes on as expected.

I think the problem is one of the following:

1. cable connected to wrong temp sender connector however the spades are different sizes and the cable is connected to the matching size (larger) one.
2. temp sender faulty/incorrect resistance: BUKH does not have any technical information available but at £74+vat+delivery its an expensive item to change without being certain.
3. thermostat opening too late: BUKH suggested a test for this but also think because the block remains touchable it is unlikely again this is a remarkably expensive item at £64 plus £12 for the o-ring +vat+delivery.
4. fouling of waterways requiring Rydlime treatment: again this seems unlikely as block remains touchable and waterflow through exhaust is plentiful.

Does anyone have any technical data or can do some resistance measurements a known working temperature sender as this is my prime suspect ?

Thanks Mort that's interesting - I assume you mean http://inadee.co.uk/fulmar.htm#Change of Distribution Plate in %20Operating%20Panel . I first noticed this after we had been on shore power for a few days and the batteries were fully topped up so think you may well be onto something there.

The thread below also states the warning light and sounder circuit should be on the smaller of the two spades, with the larger one supposed to connect to a temperature readout which mine does not have. Can you confirm this ?
http://www.ybw.com/forums/showthread.php?325540-BUKH-DV20-Temperature-sender-Faulty

Before getting involved with the distribution plate I would definitely check out the possibility that the warning light is connected to the wrong terminal of the temperature sensor.

One terminal, as you observe, has a resistance to earth which varies as the temperature varies ...... This is the connection for a temperature gauge.

The other terminal is the switch for the warning light and buzzer. It will normally be an open circuit until the "overheat" temperature is reached. Then it will close and the light and buzzer will be activated.

It would be wise to remove the sensor and test it to ensure that the switch does in fact close under overheating conditions. Unfortunately I cannot see the temperature at which this switch should close specified in the workshop manual.

 

[winsbury]

If that is the case it is definitely on the wrong spade but also has the wrong female connector on it, I wonder why ?

From memory the previous owner said he had recently replaced the alternator and never used shore power as he was 'a real sailor that didn't use marinas' so the batteries were usually not fully charged so quite possibly he never experienced this issue or if he did he certainly didn't tell me about it. During the survey test the engine was run up to temperature and neither I not the surveyor noticed any (feint) alarm then but the batteries were less than full. The plate was not on my hit list but I will definitely be taking a closer look now to see if its the correct one for the alternator; less than a fivers worth of bits from RS components to fix makes it a no-brainer to try.

Its a pity there isn't more information about the sensor though, it would be good to know the spec to test it properly as you say.

 

[VicS]

If that is the case it is definitely on the wrong spade but also has the wrong female connector on it, I wonder why ?

It struck me as curious that you have the dual sensor but no temperature gauge. A simple overheat warning switch is shown in the wiring diagrams for engines without a gauge. there is no indication of the type/size of the connectors though

You do not know who has meddled with things in the past or what they have done.

It expect the switch to operate below 100C so I'd check it in boiling water

 

[winsbury]

That's was expecting too; a bimetallic switch is all that it needs to sound an alarm at a preset temperature.

http://www.howardinstruments.com.au/userfiles/files/Viewline_Marine_Catalogue.pdf page 34 shows the VDO temperature senders specifications and pinout. I think the BUKH part is just one of these re-badged judging by this thread http://www.seabreeze.com.au/forums/Sailing/General/Buhk-Diesel-VDO-sender-units-twin-terminal/ . The catalog clearly shows the 6.3mm spade as the switch for alarm and the 4.8mm one as the varistor for a temperature gauge. Since its not a pressurised water cooling system I would imagine the switching point must be below 100C too.

I'm coming around to the idea that the cable was simply on the wrong connector in spite of the mis-match in sizing. Heating the sensor to 100C will prove that to my satisfaction I think.

 

[sgr143]

I had a slightly similar problem on the DV20 on my boat. The alarm sounder kept going off even though the engine was clearly not overheating. I checked the sender and found that it was defective (and so replaced it). The part is a VDO 803/1/23 (Furneaux& Ridall Ref: 323-803-001-023); cheaper from F&R than Bukh if you need a new one (http://www.furneauxriddall.com/acat...Return-M14-with-80-C-W-C-323_803_001_023.html ). The smaller terminal is the one that is used to activate the alarm; it does so by grounding the terminal to the body of the sender - it should do so at 80C. The larger one runs a temperature gauge, if you have one (I don't). In your case it looks like you probably don't need a new sender: just swapping the wire to the correct terminal should do the job.

Having put in the new sender, I also Rydlymed the engine and checked the thermostat operation temperature (60C) for good measure. All is now fine.

Steve

 

[winsbury]

That's a much better price for the sender, nice one.

 

[winsbury]

Removed the old sender with 19mm ring spanner and stood it in a pan of water while it heated; resistance on large spade to body of the device decreased with temperature while the small spade stayed open circuit until around 80C then it shorted and reopened when the temperature dropped. So, I'm happy it is working as anticipated. Thanks for your help folks.

 

[mievan]

I have a similar problem with the alarm. Yesterday I ran the engine while on my mooring and after 20 mins the alarm sounded. There was no debris in the inlet and plenty of water coming out the exhaust. The engine did not feel hot to the touch. Today I replaced the impeller and the engine ran for 1.5 hours. The alarm came on twice for a second only during that time. So does it mean I may have a faulty intermittent VDO?

 

[chriswesterman]

Had similar problem with the VDO sensor causing alarm to produce low level alarm on DV20 . Whilst the sender tested Ok in a saucepan there was a small split in the casing which was causing the problems probably letting water . Replacement fixed the problem